Device for indicating the passage of a train



y 1966 J. Foss ETAL 3,

DEVICE FOR INDICATING THE PASSAGE OF A TRAIN Filed Aug. 15, 1962 INVENTQRI JACQUES FOSSE LOUIS DESPREZ BYMQNT.

United States Patent 3,259,741 DEVICE FOR INDICATING THE PASSAGE OF A TRAIN Jacques Foss, Argenteuil, and Louis Desprez, Paris,

France, assignors to North American Philips Company,

Inc., New York, N.Y., a corporation of Delaware Filed Aug. 13, 1962, Ser. No. 216,425 7 Claims. (Cl. 246-250) The invention relates to a device for indicating the passage of a train travelling in a given direction.

Such a device may be used for controlling semaphores or railway barriers at level crossings. The device should only become operative .when a train approaches a level crossing, whereas it should not become operative, when the train travels in the opposite direction since in this case the train has already passed the level crossing.

Known devices of the kind set forth comprise, as a rule, mechanically moving parts which are moved by the train into a given position and thus control a switch. In practice, even though extreme care is taken in the design and construction of these devices, they do not meet the highest requirements of reliability, and damage thereto frequently occurs.

There is already known a device in which an oscillator is arranged along the railway track so that it is acted upon at a given distance by given parts of the .train, for example, the :wheels. The output signal of the oscillator is supplied to an indicating member. The oscillator may be damped by the train so that the output signal disappears or is at least reduced to a given value so that it cannot pass via a threshold device. As an alternative, the oscillator may be detuned so that the output signal has a different frequency and can be cut off by a filter. This device does not comprise mechanically moving parts directly controlled by the .train. There is a further advantage that said device operates on a rest current, which means that normally the indicator receives a signal which disappears both in the presence of a train and upon the occurrence of any component failure in the system or the drop-out of the supply voltage so that a malfunction in the system cannot give rise to accidents. With a View to safety, it is preferable to give an erroneous indication of .the presence of a train, which is not there in reality, over the non-indication of the real presence of a train.

The invention has for its object to improve such an electronic train indicator so that an indication is given only when a train travels in a given direction, whereas no indication is given for the opposite direction of travel.

Also in this case the safety requirements are prevalent, which means that, when a failure occurs, there must be given an indication as if a train passes in the given direction, even if the train passes in the opposite direction.

In accordance with the invention, a first oscillator has arranged in its proximity a second oscillator, which can be acted upon by a passing train. The output signal of the second oscillator is supplied to a monosta ble circuit so that when a train passes, the monostable circuit is switched, under the control of the output signal of the second oscillator, from the rest or stable condition into the operative or unstable position and thus actuates an auxiliary oscillator. The output signal of the auxiliary oscillator is superimposed on the output signal of the first oscillator.

When a train first passes the second oscillator, the auxiliary oscillator will feed a signal -to the indicating device at the instant when the train passes by the first oscillator, so that the drop-out of the output signal of the first oscillator is, so to say, masked by the output signal of the auxiliary oscillator. The auxiliary oscillator must therefore remain operative after the train has passed the ice second oscillator, at least for a time such that the period in which the train acts upon the first oscillator is bridged. The time during which the auxiliary oscillator remains operative is determined by the monostable circuit, which is formed by a device which is normally in a given rest position and which can be brought into an operative position, from which it returns automatically into the rest position after a certain period of time. The restoring time may, in principle, have a predetermined, fixed value, but it is preferably variable so that the said time, which corresponds with the time of operation of the auxiliary oscillator, is shorter according as the speed of the train is higher, so that the time required by the train to pass by the first oscillator is shorter.

The device is therefore constructed preferably so that the monos-table circuit comprises a capacitor which is charged during the time in which the second oscillator is acted upon by given parts of the train, while the auxiliary oscillator is rendered operative during the discharge period of the capacitor.

The invention will be described with reference to the drawing, wherein:

FIG. 1 shows diagrammatically one embodiment of the invention. FIG. 2 shows an embodiment of a monostable circuit suitable for use :with the apparatus of FIG. 1 in which the restoring time depends upon the speed of the train. FIG. '3 shows another embodiment of a monostable circuit and the auxiliary oscillator controlled thereby, in which device there are taken a number of measures to insure reliable operation.

The system shown in FIG. 1 comprises two oscillators G and G arranged in close proximity to the rails RC so that the train wheels pass by in close proximity thereto and can act upon the oscillators by inductive or capacitative effects so that these oscillators are, for example, damped. In the position W of a wheel the generator G will be damped, for example, and in the position W the generator G is damped, whereas in an intermediate position W no influence is exerted on either oscillation generator G or G As a matter of fact, the influence is not only exerted in one given position of a wheel but over a given section.

The oscillator G normally supplies an alternatingvoltage signal to the indicating device ND. The wheels of a train travelling from right to left in the direction of arrow D will first pass by the generator G and then the generator G so that these oscillators are damped a short time one after the other. The indicating device ND responds in known manner to the disappearance of the output signal of the generator G and then performs further control operations in known, irrelevant manner. A short time later, the generator G will be damped, it is true, but as will be seen hereinafter, this has no further consequences with respect to the indication of the train, since at any rate the signal fed to the indication device ND is interrupted, at least for a given period.

The output signal of the generator G is normally supplied via the device VD, formed, for example, by an amplifier and a rectifier, to the monostable circuit M. If a train travels from left to right in the direction of the arrow D the wheels will first pass by the generator G and a short time afterwards by the generator G This results in the interruption of the output signal of the generator G for a given period of time. Consequently, the monostable circuit M is switched from the rest position into the operative position so that the auxiliary oscillator OS is rendered conductive. The generator OS then supplies an alternating-current signal to the indicating device ND for the time during which the monostable circuit is in the working position. When the wheels of the train reach the generator G a short time afterwards,

Patented July 5, 1966 this generator will also be damped, so that the output signal disappears, but this no longer has any influence, since during this time the indicating device ND receives a signal from the oscillator OS. To this end the auxiliary oscillator OS is required to remain operative for a sufiiciently long time after the generator G has been passed by, until the signal of the generator G reappears.

To this end, in principle ,a sufiic-iently long restoring time could be provided for the monostable circuit, but this involves difiiculties in view of the fact that the trains may have highly different speeds. The restoring time must be chosen in accordance with the expected minimum speed. However, not only the passage of the first wheel of a train travelling in the direction D but also the passage of the further wheels should be masked with the generator 6,. If the restoring time of the monostable circuit is comparatively long, there is the risk that the monostable circuit should just return to the rest position at the instant when a further wheel passes by the generator G while it cannot be brought back sufficiently rapidly to the working position to supply a masking signal via the oscillator OS to the indicating device ND.

With a view thereto it is desirable to adapt the restoring time of the monostable circuit M to the speed of the train.

In the arrangement shown in FIG, 2, the collectors of the transistors T and T and the base of the transistor T are connected via resistors R R and R to a negative voltage source V, whereas the emitters are connected to ground. The device VD normally supplies a negative direct voltage to the base of the transistor T The two transistors are conductive in this state and the potentials at the points a and b are substantially equal to ground potential so that the capacitor C connected between the collector of the transistor T and the base of the transistor T is not charged. When a wheel of a train passes by the oscillator G the negative voltage at the base of the transistor T disappears and the transistor is thus blocked. The capacitor C is then charged in a circuit from ground via the emitter and the base of the transistor T (which thus remains conductive), the capacitor C and the resistor R to the negative voltage source -V. During the charging period the voltage at point b remains substantially equal to ground potential, whereas the potential at point a becomes more negative. Charging is continued as long as the oscillator G is clamped by the wheels and the final charge of the capacitor C will be the higher the longer is the charging period, i.e. the lower is the speed of the train. After the wheel has passed by the oscillator G the latter again supplies a signal to the amplifier VD, which again supplies a direct output voltage to the base of the transistor T which thus becomes conductive. The voltage at point a then rises to ground potential, whereas the voltage at point b rises by the same amount and thus becomes positive with respect to the emitter of the transistor T which is thus blocked.

The auxiliary oscillator OS is controlled by the voltage at the collector of the transistor T so that the oscillator oscillates and supplies a signal to the indicating device ND when the transistor T is cut ofi. The capacitor C then is discharged in the circuit from ground via the emitter and the base of the transistor T the capacitor C and the resistor R to the negative voltage source V. After the capacitor C has been discharged, the transistor T again becomes conductive and the oscillator OS is blocked. The discharge time is the greater, the higher has been the initial charge of the capacitor C or the lower is the speed of the train.

The simple arrangement shown in FIG, 2 has the disadvantage that fail-safe operation is not obtained under all conditions. The arrangement must be such that, in the event of a disturbance, the oscillator OS cannot become operative, since it would then also mask the passage of a train in the direction of the arrow D which, of course, is inadmissible. In the arrangement shown in FIG. 2, for example, a breakage of the resistors R or R or a short-circuit between the base and the emitter of the transistor T would have the same effect as if the transistor T were blocked and the oscillator OS became operative.

In the arrangement shown in FIG. 3, the masking oscillator OS is controlled via two different circuits so that at points P and Q given voltage variations are required for the oscillator to become operative. Consequently, if a disturbance occurs in one of the circuits, only the voltage at one of these points will vary, which is not sufficient to turn on the oscillator.

The arrangement partly corresponds with that shown in FIG. 2 with respect to the transistors T and T the capacitor C and the resistors R R and R The transistors T and T are also in this case normally conducting. The collector of the transistor T is connected via a resistor R to the base of a transistor T The emitter of T is grounded. The collector of the transistor T is connected to the control-point P of the oscillator OS and is furthermore connected via a resistor R to the supply source -V. In contrast to the arrangement shown in FIG. 2, the upper end of the resistor R is not connected directly to the supply source V, but via the resistor R The arrangement comprises a second circuit for controlling the voltage at point Q. The second circuit corresponds completely to the arrangement of the capacitor C and the transistor T The capacitor C the resistors R and R and the transistor T correspond with the capacitor C the resistors R and R and the transistor T and the operation is completely the same. The transistors T T and T are normally conducting. The transistor T is normally blocked since the voltage at the base and at the emitter is approximately equal to ground potential.

If a wheel of a train passes by the oscillator G the transistor T is blocked, as is described with reference to FIG. 2, so that the capacitors C and C are charged via the emitter-base circuits of the transistors T and T and the series-connected resistors R and R As soon as the wheel has passed by, the transistor T again conducts so that the potentials at points a, b and d rise and the transistors T and T are blocked. The blocking of the transistor T causes the potential at point Q, which is normally equal to ground potential, to become negative. Owing to the blocking of the transistor T the voltage at the base of the transistor T goes negative. Transistor T thus becomes conductive and the potential at point P, which normally has a negative value, rises to ground potential. The function of the transistor T consists, in the first place, of inverting the voltage variation across the collector of the transistor T (which has the same sense as that of the collector of transistor T so that the voltage variations at points P and Q are relatively opposite, which means that the voltage at point P rises, whereas that at point Q drops so that the voltage between these points reverses its polarity. Since the point P assumes ground potential, the supply voltage at the collector of the transistor T disappears, but this has no direct consequences, since this collector, even in the conducting state of the transistor, is at ground potential.

The oscillator OS comprises a transistor T the emitter and the collector of which are connected via windings L and L of the transformer TR to the points P and Q. The base is connected to point B of the voltage divider R R which is connected between the supply source V and ground. The winding L and the capacitor C constitute a frequency-determining feedback circuit. The winding L provides a feedback so that the oscillator starts oscillating in known manner provided the transistor receives the appropriate supply voltage, which means that the emitter must be positive with respect to the base and the collector must be negative, since otherwise the transistor is not conducting or does not amplify. This means that the points P and Q must be positive and negative, respectively, with respect to point B of the voltage divider R R The oscillator will thus start oscillating if, as described above, the transistor T becomes conducting and the transistor T is blocked.

The capacitors C and C then discharge via the transistor T and the resistors R and R after which the transistors T and T again become conducting and the transistor T is blocked. The point P once again assumes a negative voltage and the point Q assumes ground potential, so that the oscillator OS is blocked and the rest position is regained.

As stated above, the oscillator OS requires for its operation that the potential at point P should be comparatively high and that at point Q should be comparatively low. In the rest position the potential at point Q is high and that at point P is low.

If a malfunction occurs in one of the transistors T and T or in the resistors connected thereto, for example, a short-circuit in the transistors or a short-circuit elsewhere or a break in the wiring, this can at the most give rise to an increase in the voltage at point P to ground potential. However,.the oscillator 05 cannot become operative as long as the voltage at point Q is high, since the collector of the transistor T is then positive with respect to the base and the transistor does not amplify. However, if due to a disturbance, for example, a short-circuit between the collector and the emitter of the transistor T the point P assumes ground potential, the collector supply for the transistor T via the resistor R is suppressed. Therefore, the eifect of this transistor disappears and the point a must remain at ground potential and the capacitors C and C can no longer be charged.

If, conversely, a malfunction occurs in the transistor T or the resistors connected thereto, only the voltage at point Q can vary. Consequently, unless a disturbance occurs simultaneously in the two circuits T T and T respectively, the oscillator OS cannot be rendered conducting.

What is claimed is:

1. A railway signal system for indicating the passage of a train in a given direction of travel along a section of railway track comprising first control means located near said track and responsive to the presence of a passing train for producing a first control signal, second control means located along said track and spaced apart from said first control means so that the train passes said firs-t control means first when moving in said given direction of travel and passes said second control means first when moving in the opposite direction, said second control means being responsive to the presence of a passing train for producing a second control signal, monostable circuit means having a stable condition and an unstable condition and responsive to said second control signal, said monostable circuit means being switched to said unstable condition by said second control signal upon passage of a train past said second control means, third control means coupled to said monostable circuit means and responsive to the switching thereof for producing a third control signal of a duration sufiicient to overlap in time the produced first control signal when said train moves in said opposite direction, indicating means, and means for supplying said first and third control signals to said indicating means so that for said opposite direction of travel said third control signal inhibits said first control signal from producing an indication on said indicating means.

2. A railway signal system for a section of railway track comprising first control means located near said track and responsive to the presence of a passing train for producing a first control signal, second control means located along said track and spaced apart from said first control means, said second control means being responsive to the presence of a passing train for producing a second control signal having a time duration which is variable and is determined by the time period during which said train passes by said second control means, monostable circuit means having a stable condition and an unstable condition and responsive to said second control signal, said monostable circuit means being switched to said unstable condition by said second control signal upon passage of a train past said second control means, said monostable circuit means further comprising timing means for maintaining said monostable circuit means in said unstable condition for a period of time determined by the duration of said second control signal whereby said monostable circuit means produces a timing control signal having a variable time duration determined-by the time duration of said unstable condition, third control means coupled to said monostable circuit means for producing a third control signal in response to the switching of said monostable circuit means, said third control means-being normally inactive and responsive to said timing control signal for producing a third control signal having a time duration determined by the time duration of said timing control signal, indicating means, and means for supplying said first and third control signals to said indicating'means.

3. A railway signal system for a section of railway track comprising first and second alternating current signal generator means located in spaced relationship along said track in eleotroresponsive coupling relationship with a passing train, a monostable circuit having a stable state and an unstable state and controlled by a signal produced by said second signal generator means upon passage of a train near said signal generator means thereby to switch said monostable circuit from said stable state to said unstable state, an auxiliary signal generator means coupled to said monostable circuit for producing an auxiliary control signal in response to the switching of said monostable circuit, said first signal generator means producing a first control signal upon passage of a train, indicating means, and means for applying said first control signaland said auxiliary control signal to said indicating means- 4. Apparatus as described in claim 3 wherein said monostable circuit comprises a capacitor which is charged during time said second signal generator means is in electro-responsive coupling relationship with a passing train and is discharged upon passage of said train out of coupling realtionship, said auxiliary generator means being rendered operative to produce said' auxiliary control signal during the discharge period of said capacitor.

5. Apparatus as described in claim 3 wherein said monostable circuit comprises first and second signal translating elements each of which includes an input electrode and an output electrode, a source of supply voltage, first and second impedance elements, means connecting said first impedance element between said output electrode of said first signal translating element and said voltage source and means connecting said second impedance element between said input electrode of said second signal translating element and said voltage source, a capacitor connected between the output electrode of said first translating element and the input electrode of said second translating element, means for coupling the signal produced by said second signal generator means to the input electrode of said first translating element, said second signal generator means producing a signal voltage in the absence of a train in the vicinity thereof which causes conduction in said first and second signal translating elements, said second signal generator means producing a change in said signal voltage during passage of a train whereby said first signal translating element is cut-off thereby causing a charge current to flow in said capacitor, said second signal generator means roducing the original signal voltage when said train has passed by thereby causing said first translating element to conduct and said second translating element to be cut-off by the charge accumulated on said capacitor, said second translating element being held cutolf until said capacitor discharges to a predetermined level, said auxiliary signal generating means being coupled to the output electrode of said signal translating element and controlled by the signal voltage produced at said output electrode so as to produce said auxiliary control signal during the period translating element is cut-off.

6. Apparatus as described in claim 3 wherein said monostable circuit comprises first, second and third transistors each having emitter, base and collector electrodes, means connecting each of said emitter electrodes to a point of reference potential, a source of supply voltage, means connecting the base and collector electrodes of said second and third transistors to said voltage source by means of individual resistance elements, first and second capacitor-s connected between the collector of said first transistor and the base electrodes of said second and third transistors, respectively, means for coupling the signal voltage produced by said second signal generator means to the base of said first transistor so that said first, second and third transistors are normally conducting in the absence of a train, a voltage inverting device having an input electrode connected to the collector of said second transistor and an output electrode, said auxiliary signal generating means comprising an oscillator having a pair of input terminals and biased such that oscillations are produced when said input terminals are supplied with given voltages of opposite polarity, means coupling the output electrode of said voltage inverting device to one of said input terminals and the collector electrode of said third transistor to the other of said pair of input terminals, said second signal generator means producing a signal voltage during the time a train is passing which cutsoff said first transistor thereby causing a charge current to flow in said first and second capacitors, said first transistor reverting to its conducting state upon passage of said train and said second and third transistors being cutolT by the charge accumulated on said first and second capacitors, respectively, said first transistor providing a discharge path for said first and second capacitors, said third transistor and said voltage-inverting device supplying said given voltages of opposite polarity to said oscillator input terminals to produce oscillation thereof dur ing the discharge time of said first and second capacitors.

7. Apparatus for indicating the passage of a trainon a section of track in a given direction of travel, comprising first oscillation generator means located along said track in electro-responsive coupling relationship with a passing train, second oscillation generator means located along said track behind said first oscillation generator means in said given direction of travel, said second oscillation generator means being in electro-responsive coupling relationship With a passing train, each of said first and second oscillation generator means having a resonant circuit for producing first and second oscillation signal voltages, respectively, in the absence of a train and being damped by a passing train thereby to reduce the amplitude of said signal produced, indicating means coupled to said first oscillation generator means and responsive to said reduced amplitude of said first signal voltage for indicating the passage of a train in said given direction of travel, a monostable circuit having a stable state and an unstable state and controlled by said second signal voltage produced in said second oscillation generator means, said monostable circuit being in said stable state in the absence of a train and being switched to said unstable state upon reduction of said second signal voltage caused by the damping effect on said second oscillation generator means by a passing train, said monostable circuit comprising a timing capacitor which controls the time duration of said unstable state proportional to the speed of said passing train, auxiliary oscillation generator means coupled to said monostable circuit for producing an auxiliary oscillation signal voltage having a time duration controlled by the time period said monostable circuit is in said unstable state, and means for applying said auxiliary oscillation signal to said indicating means, said auxiliary signal preventing operation of said indicating means for the direction of train travel opposite to said given direction of travel.

References Cited by the Examiner UNITED STATES PATENTS 2,105,930 1/1938 Reichard 246-249 2,355,395 8/1944 Rubenstein. 3,177,359 4/1965 Bramer et a1. 246--77 X FOREIGN PATENTS 225,563 8/ 1958 Australia. 1,203,211 7/1959 France.

ARTHUR L. LA POINT, Primary Examiner. LEO QUACKENBUSH, EUGENE G. BOTZ, Examiners. S. B. GREEN, Assistant Examiner. 

1. A RAILWAY SIGNAL SYSTEM FOR INDICATING THE PASSAGE OF A TRAIN IN A GIVEN DIRECTION OF TRAVEL ALONG A SECTION OF RAILWAY TRACK COMPRISING FIRST CONTROL MEANS LOCATED NEAR SAID TRACK COMPRISING FIRST CONTROL MEANS LOCATED NEAR FOR PRODUCING A FIRST CONTROL SIGNAL, SECOND CONTROL MEANS LOCATED ALONG SAID TRACK AND SPACED APART FROM SAID FIRST CONTROL MEANS SO THAT THE TRAIN PASSES SAID FIRST CONTROL MEANS FIRST WHEN MOVING IN SAID GIVEN DIRECTION OF TRAVEL AND PASSES SAID SECOND CONTROL MEANS FIRST WHEN MOVING IN THE OPPOSITE DIRECTION, SAID SECOND CONTROL MEANS BEING RESPONSIVE TO THE PRESENCE OF A PASSING TRAIN FOR PRODUCING A SECOND CONTROL SIGNAL, MONOSTABLE CIRCUIT MEANS HAVING A STABLE CONDITION AND AN UNSTABLE CONDITION AND RESPONSIVE TO SAID SECOND CONTROL SIGNAL, SAID MONOSTABLE CIRCUIT MEANS BEING SWITCHED TO SAID UNSTABLE CONDITION BY SAID SECOND CONTROL SIGNAL UPON PASSAGE OF A TRAIN PAST SAID SECOND CONTROL MEANS, THIRD CONTROL MEANS COUPLED TO SAID MONOSTABLE CIRCUIT MEANS AND RESPONSIVE TO THE SWITCHING THEREOF FOR PRODUCING A THIRD CONTROL SIGNAL OF A DURATION SUFFICIENT TO OVERLAP IN TIME THE PRODUCED FIRST CONTROL SIGNAL WHEN SAID TRAIN MOVES IN SAID OPPOSITE DIRECTION, INDICATING MEANS, AND MEANS FOR SUPPLYING SAID FIRST AND THIRD CONTROL SIGNALS TO SAID INDICATING MEANS SO THAT FOR SAID OPPOSITE DIRECTION OF TRAVEL SAID THIRD CONTROL SIGNAL INHIBITS SAID FIRST CONTROL SIGNAL FROM PRODUCING AN INDICATION ON SAID INDICATING MEANS. 